Vacuum cut-off switch



July 14', 1964 J. E. COYLE VACUUM CUT-OFF SWITCH w I m Filed June 18,1962 INVENTOR. r/MP/l 5. C 5' III FIEZ

United States Patent 3,140,819 VACUUM CUT-OFF SWITCH Joseph E. Coyle,Arlington, Mass, assignor to the United States of America as representedby the Secretary of the Air Force 7 Filed June 18, 1962, Ser. No.203,416 4 Claims. (Cl. 230-18) This invention relates to a protectivedevice for vacuum systems and is more particularly concerned withproviding a cut-off switch for detecting relatively large leaks in avacuum system and responding by cutting off the flow of current to thevacuum pump motor in order to prevent serious damage to the pump.

Various vacuum gauges have long been in existence as a means ofdetecting small leaks in vacuum systems. These gauges ordinarily operatein the limited range of approximately 5 to 500 microns of mercury andare useful for detecting small leaks and to allow partial vacuum to bemaintained by the pump until the leak can be discovered. Although thisarrangement is useful in the detection and repair of small leaks, othermore serious problems come about when a large leak occurs in the vacuumsystem. If the pump is operating and a large leak suddenly occurs, thevacuum cannot be maintained at a safe, effective level and usuallyserious damage results to the system, particularly to the vacuum pumpelement.

Accordingly, it is an object of the present invention to provide avacuum cut-off switch that will operate in a range upward ofapproximately 5 cm. of mercury which is far beyond that of presentlyknown small leak detecting gauges.

Another object of the invention is to provide a protective device for avacuum system which would only be responsive to large leaks in thesystem and operate to break the flow of current to the forepump andthereby protect the system from damage.

A further object of the invention is to provide a pressure responsivedetecting means associated with a switching means for controlling theoperation of a vacuum system.

A still further object of the invention is to provide a vacuum cut-offswitch that is adjustable to respond to a predetermined drop in vacuumpressure. Biasing means are provided to prevent operation of the switchas a result of the normal variations in atmospheric pressure.

These and other objects, features, and advantages will become moreapparent after considering the following detailed description taken inconjunction with the annexed drawings and appended claims.

In the drawings, wherein like reference characters refer to like partsin both views:

FIGURE 1 is a view in crosssection of the vacuum cut-off switch designedand constructed according to the invention; and

FIGURE 2 is a schematic view of the cut-off switch in position in atypical vacuum system.

Referring now to FIGURE 1, there is shown the vacuum cut-off switch 13having a pressure responsive mem her in the form of an expansiblecorrugated metallic bellows 15 suitably mounted on a plate 17. The otherend of the bellows 15 is fixedly attached to the lower face of thecut-off switch cover plate 19. A hollow stem portion 21 is attached tothe upper face of the cover plate 19 and communicates with the interiorof the bellows 15 through an aligned opening in the cover plate 19.

A threaded sleeve 23 is attached to the cover plate 19 and extendsdownwardly around the outside of the bellows 15. A pressure selectorring 25 engages the threads on sleeve 23 and moves downwardly orupwardly to exert more or less force on the mounting plate 17 3,140,819Patented July 14, 1964 through a biasing spring 27. The lock ring 29serves to maintain the pressure selector ring 25 in position on thesleeve 23 after the adjustments have been made. Openings 31 are providedin the upper body portion 33 of the cut-off switch 13 in order to allowfor pressure differential adjustments. Stop members 35 are attached tothe body portion 33 and serve to engage the lower surface of themounting plate 17 to limit the downward movement of the bellowsassembly. A boss 37 is provided on the lower surface of the mountingplate 17 and extends downwardly therefrom.

A normally closed microswitch 39 is mounted in the base portion 41 andextends upwardly into the body portion 33. The button element 43 of themicroswitch 39 is located in close proximity to the boss 37 so thatdownward movement of the bellows assembly and mounting plate 17 engagesthe button 43 and causes the electrical circuit to be opened, therebycutting off the flow of current to the vacuum pump motor circuit. Thumbscrews 45 are provided for adjusting the vertical position of themicroswitch 39 in relation to the bellows assembly in order to controlthe cut-off action of the switch 13.

In FIGURE 2, there is shown a diagrammatic view of the vacuum cut-offswitch 13 in conjunction with a vacuum system to be controlled thereby.The conduit 47 leads from the evacuation chamber 49 to the vacuum pump51 driven by the motor 53. A power source 55 feeds the windings of themotor 53 and passes through the normally closed microswitch 39 shownmore clearly in FIGURE 1.

In operation, the normal position of the cut-off switch 13 is indicatedin the view shown in FIGURE 1. As shown, the normally closed microswitch39 is out of contact with the boss 37. In this position, the current isflowing to the pump motor 53 and the pump 51 is operating to generateand maintain a vacuum in the chamber 49. The bellows 15 is drawn andheld upward because of the negative pressure therein and, as a result,the biasing spring 27, is held in a compressed state. If a large leakshould develop in the chamber 49, the resulting pressure rise would becommunicated to the bellows 15 through the conduit 47. This would causethe bellows 15 to move downward because the pressure differentialtherein would be reduced and the biasing action of the spring 27 wouldbe the dominant force acting on the mounting plate 17. As the abovesequence of events occurs, the boss 37 contacts and depresses the button43 which instantaneously cuts off the flow of current to the motor 53,thereby stopping the rotation of the pump 51. Thus, any damage which mayresult to the forepump 51 or the material in the evacuated chamber 49because of the continued operation of the pump after a large leakdevelops, would be prevented by the action of the cut-off switch 13.

After the leak in the vacuum system has been located and repaired, thesystem can be restarted by manually shunting the energizing currentdirectly to the pump motor causing the system to become evacuated andthe cut-off switch 13 will automatically be in condition to operateagain to protect the system from possible damage. In other words, noresetting or replacing of parts in the vacuum cut-off switch isnecessary in order to rEstore the switch to operating condition.

As shown and described, the switch is directed toward a protectivedevice to prevent damage to a vacuum pump. However, it can be seen thatthe device is useful in many other applications in vacuum systems. Forexample, the switch could be used to cut off the fiow of current to aunit in the evacuation chamber, if this were desirable or necessary whenthe vacuum reading reached a particular range.

Although the invention has been described with reference to a particularembodiment, it will be understood to those skilled in the art thatvarious changes and modifications can be made therein without departingfrom the invention. Therefore, it is intended that all matter containedin the above description and shown in the accompanying drawings shall beinterpreted in the illustrative sense, and it is aimed in the appendedclaims to cover all such changes and modifications without departingfrom the true spirit and scope of the invention.

What is claimed is:

1. A protective device for controlling the operation of a motor drivenvacuum system, said device comprising an evacuated chamber, a pressureresponsive bellows means having a single opening therein incommunication with said evacuated chamber, said bellows means being heldin contracted position by the pressure difierential therein, adjustablespring biasing means surrounding said bellows means for urging saidbellows means into expanded position, and switch means operativelyassociated with said bellows means to be actuated thereby, the expansionof said bellows means on the urging of said biasing means causing theactuation of said switching means thereby resulting in the opening of anelectrical circuit to cause cessation of the flow of current to thedrive motor.

2. The control device defined in claim 1 wherein balancing means areprovided for varying the applied expansion force on said bellows meansthrough said biasing means, the applied load being dependent upon theprevailing atmospheric pressure.

3. The control device defined in claim 1 wherein means are provided forvarying the position of said 4 switching means in relation to saidbellows means thereby correspondingly varying sensitivity level of saiddevice.

4. A protective device responsive to a rapid change of pressure in amotor driven vacuum system, said device comprising an expansiblecorrugated pressure responsive bellows means having its interior indirect communication with an evacuated chamber, one end of said bellowsmeans being fixedly attached to a cover plate and the other end beingfixedly attached to a movable plate defining a sealed chamber ofvariable volume having a single opening therein, switching meansdisposed in close proximity to the movable plate end of said bellowsmeans, and adjustable spring biasing means surrounding said bellowsmeans for urging said bellows means into contact with said switchingmeans in response to a rapid change of pressure in the evacuatedchamber, said switching means operating to disconnect the motor from thepower supply of the vacuum system.

References (Iited in the file of this patent UNITED STATES PATENTS334,890 ODonel Jan. 26, 1886 1,231,561 Briggs July 3, 1917 2,601,757Horton July 1, 1952 2,695,764 Burlingham Dec. 21, 1954 2,765,743Hollinshead Oct. 9, 1956 2,768,646 Plank Oct. 30, 1956 3,049,602 FlattAug. 14, 1962 3,049,603 Flatt Aug. 14, 1962 FOREIGN PATENTS 1,135,558France Apr. 30, 1957

1. A PROTECTIVE DEVICE FOR CONTROLLING THE OPERATION OF A MOTOR DRIVENVACUUM SYSTEM, SAID DEVICE COMPRISING AN EVACUATED CHAMBER, A PRESSURERESPONSIVE BELLOWS MEANS HAVING A SINGLE OPENING THEREIN INCOMMUNICATION WITH SAID EVACUATED CHAMBER, SAID BELLOWS MEANS BEING HELDIN CONTRACTED POSITION BY THE PRESSURE DIFFERENTIAL THEREIN, ADJUSTABLESPRING BIASING MEANS SURROUNDING SAID BELLOWS MEANS FOR URGING SAIDBELLOWS MEANS INTO EXPANDED POSITION, AND SWITCH MEANS OPERATIVELYASSOCIATED WITH SAID BELLOWS MEANS TO BE ACTUATED THEREBY, THE EXPANSIONOF SAID BELLOWS MEANS ON THE URGING OF SAID BIASING MEANS CAUSING THEACTUATION OF SAID SWITCHING MEANS